Linear accelerator



5 Sheets-Sheet 1 L. W. ALVAREZ LINEAR ACCELERATOR mili-L March 20, 1951 Filed May 2e, 1947 OSC/LLA TOR 7 VOLTAGE VOLTAGE' March 20, 1951 L. w. ALVAREZ LINEAR ACCELERATOR 5 Sheets-Sheet 2 Filed May 26. 1947 WN WQ /NVENTOR U/J M/ A1. VA REZ A 7 TOR/VEK March 20, 1951 l.. W. ALVAREZ LINEAR ACCELERATOR 5 Sheets-Sheet 5 Filed May 2ec 1947 ih. L

A Tron/Vey,

March 20, 1951 L. W. ALVAREZ LINEAR AccELERAToR 5 Sheets-Sheet 4 Filed May 26, 1947 A Tron/VEZ March 20, 1951 l.. w. ALVAREZ 2,545,595

LINEAR ACCELERATOR Filed May 26, 194'? 5 Sheets--SheetI 5 /NVENTOR .L1/As` MALI/,4R52

A TroR/ws n Patented Mar. 20, 1951 LINEAR ACCELERATOR Luis W. Alvarez, Berkeley, Calif., assignor to the United States of America as represented by the United States Atomic Energy Commission Application May 26, 1947, Serial No. 750,598

11 Claims.

This invention relates to a method and apparatus for ion acceleration at high energies and more particularly to an ion accelerator utilizing the energy of electric fields in a resonant cavity to accelerate ions in quantity.

Heretofore long cylindrical cavities, or wave guides, excited to permit the formation of standing waves therein having a very high node to node impedance and electrically loaded so that an electron traveling along the axis at the velocity of light would experience a force which is always in the forward direction, have been used for electron acceleration. However, with ions 'the case is quite different as it is not possible to load a wave guide so that the wave velocity will be as slow as that of ions. and consequently such wave guides are impractical for use for ion acceleration.

Now it has been found, that by exciting a long cylindrical cavity, or wave guide in the axial electric mode and placing coaxial drift tubes at regular intervals along the axis of the guide, forming a sequence of gaps, ions will be accelerated therethrough if the drift tubes are at the proper spacing to act as shields to protect the ions from the reverse potential which occurs every half cycle of the exciting frequency as the lion progresses along the axis of the guide.

Thus an ion traveling along the axis of such a wave guide will receive an acceleration in one gap and travel through a drift tube while the fields are reversed and arrive at the next gap when the nelds are in the proper phase.

The ions will therefore enter this new field when it is in a proper direction to accelerate them in the same direction as they were accelerated in the gap traversed one cycle earlier. In this manner ions can be made to serially traverse a sufficient number of gaps to give them a total acceleration which will impart the desired energy.

The above elucidated concept has been embodied into a practical, device for accelerating ions to energies as high as forty-live million electron volts.

It is therefore the object of this invention to provide a linear ion accelerator of simple f structure. f

Another object of this invention is to-provide y an ion accelerator capable of producing an effective ion beam accelerated to a velocity at whichl the energy `is of the order of many million electron volts.

Another object of this invention is to provide l a sectional ion accelerator, which, when energized, will produce ion acceleration .in accordance with the amount of power supplied and the number of sections.

Another object of this invention is to provide an ion accelerator with means of producing electric elds in the proper mode to create ion acceleration therethrough.

Another object of this invention is to provide an ion accelerator capable of maintaining ions in proper phase during the entire acceleration period.

Another object of this invention is to provide an `ion accelerator with drift tubes to shield the ions during the reverse half of the cycle.

Another object of this invention is to provide an ion accelerator with means of using metallic fois to focus the ion beam.

Another object of this invention is to provide a simple, eicient and readily constructedion accelerator, whereby ions can be eiectively accelerated to forty-five or more million electron volts for use in nuclear research or for similar purposes.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings, in which, i

Figure 1 is a diagram showing a normal cylindrical wave guide and the axial electric field distribution therein.

Fig. 2 is a diagram showing a wave guide and the electric fields when a series of graded drift tubes are placed therein.

Fig. 3 is a diagram representing the voltage existing across the gaps of the drift tubes.

Fig. 4 is a diagrammatic longitudinal sectional view of drift tube ends with the electric eld distribution existing across the gap.

Fig. 5 is a diagrammatic longitudinal section view of drift tube ends with a focusing foil attached to one tube, and the resulting electric field distribution. v

Fig. 6 is a plan view of one practical embodiment of the invention along with a multiplicity of oscillators adapted to energize the accelerator.

Fig. 7 is a longitudinal sectional view of the accelerator taken as indicated by section lines 1-1 in Fig. 6.

Fig. 8 is an enlarged section view of the target dial: and? ci? zero` Value on. the. axis'.

.- an; oscillator4 l;

Fig. 11 is a fragmentary view of a drift tube,

being generally cross section.. tillepl'ane-.of which is indicated'byV the lineA l I-i l" of-'Fig-. 7.

Fig. 12 is a fragmentary view that is compa.-

rable to a section on a plane indicated by the line |2|2 of Fig. l1, disclosing the two end. dritt.-

tubes.

Fig. 13 is a. sectional viewshowingv the details of an energizing loop, a portion offthetransmission line beiner broken away to reduce the-sizeof the illustration.

Fig. 14 is a isometric perspective showing the entire accelerator and oscillators with partA ofthe vacuum tank broken away to disclose the f inner cavi-ty and. driit, tubes..

Referring directly to the drawingsor a; more detailed; discussion andA description, of the ini/:en-

andi'rst, referring to Figi. ntl-1ere is: shown .ai conventional: elongated'. cylindrical. Wave guidel, excited by a power; source-at the. prop-crirequency' to producei an axial.` elec-tric` el'df distribution-r therein. through a; coup-lingd loop- 2, in whichi. thremagnetic. eld isz. circumferential and the field longitudinal. At the ends of the-- wave guide.. the longitudinal current. flow. becomes ra- The critical frequencyv at. which this field' distribution takes placeis. the only frequency for which thisv patterncanoccur for a given siZewave guide.

However, in a waveguide of the length` and formshown in Fig. 1:, the frequency willI be too -highf for a-nion to4 travelfrom one end-v oif the wave guide to theother whilethev axialI electricfieldl is in the proper direction. Therefore; in

' order tokusel a long wave-guide, it is necessary to add a series of coaxial tubes along theaxis as -shown-iniliigg. Zier-ming: a series-oi? gaps of appro- Yhaving coaxial drift tubes; may-1 bemade on the basis thatl the guide consists of a numberof reentrant cavities.

Nowreferringmore particularly'to Fig; 2, there i's1shown a section viewof acylindrica-lf Wave guide 3, with a series ofdrifft tubes 4'. The-wave guide can beenergized byf an oscillator output transmission line; 6'. entering wave guide 3. from An oscillator output transmis- Sion l-inecomprises. an outer conductor- 8 attached to wave guide ",E and ani innen-conductor 9: enterznei thev were.4 guide as: alcootl; and@ returning te. contact. out-er conductor 8f.

Itvmay be` preferable-tense only one-high power oscillator and one coupling, loop. for exciting hwaveauide, however, anumbet i lower power. oscillators alongwith the,y number of coupling 1912195; Elf-iced. atA conyenient, locations. along. the were.. guilde may beutlizedwith the same results. Bower atA the resonantffrequency can now be supplied to the wave guide from oscillator l" with the result that a strong electric ield is produced acrossthe gaps of; the drift tubes.

will be accelerated during such passage if properly phased with the radio frequency cycle. The entering ions will remain in proper phase with the radiofrequency cycle since each drift tube is made proportionately longer than the one preceding it, and thus the ions pass through longer and longer drift tubes as they gain in speed. In keeping with.; the above,7 it is` clear; thaty acceleration of the ions could' be theoretically continued indenitely. Furthermore, the rate oi the acceleration of ions throughout the entire accelerator is-T maintained uniform by decreasing the diameter of the drift tubes as their length is increased. This decrease in the diameter of the longer drift tubesestablishes the axial electric mod-e or oscillation uniformly throughout the length of the wave guide when varying length drift tubes are used. Y

In Fig. 3 there is shown a graph representing the voltage existing across any one drift tube duringone radio-bequemer cycle.. While: it is desirable; to have the` ions cross; the drift. tube gaps. at the.' peak or thef radioef-requency cycle, in order tolreceivefrnaximum.energy-gaioper gap, it is also necessarythatthef ions; remain in p hase with the.. radio-frequency.' cycle: during.- the.- entire; acceleration period..

I-tf.- being. necessary that. theions be. kept in phase.- during the entire: accelerationperiod., they areinj ected into. the accelerator; before; the;- peak of: the. radioefrequency cycle. as'` shown in Eig.. 3. Therefore.. ions arriving' at. the drifttube gap late with; respect to.- the selected point of admission will loe-subjected to.- a higheraccelerating potential ions arriving,v early with` respect; to the selected point: of admission will' be subjected tu a loweraccelerating potential.

It is obvious from the foregoing that. phase stability` will be attained: during the entire acceleration. periodi, because ions that are lagging with respect to. the selected point ot admission wili' be accelerated faster by-virtue oi' the higher accelerating.- potential'- across. the drift tube gap and: conversely leading ionsv will notbe. subjected to'` ashigh an accelerating potential.

Referring new` to. Fig. le there is-.show-n` a cross section. of" the ends or' adjacent drift tubes` with the electric i'eldt distribution. across them shown asdotted' lines. The graphabove the drift tube ends. represents. the. voltagel curve with respect to time; as the ions; crossv the dritt tube gap. When ions are in phase travelingY along the ayis of the drift tubes-in the direction; of the arrows, the rst half or the gap comprises a focusing region and the'. second.` halfl offthe gap-v ai. defocusing region. Since the. voltage; is. increasing' with respect to time while the ionsare in. flight across the: gap, the. defocusingV is. more pronouncedi than.. the focusing. This is. offset', butto a negligible degree, by-the shorter time of flight-for the second half ot the-distance..

In. order;Y to. ac'lfii'eve` an; overall iocusingy action arthin metallioioil. Ik is: placed over the entered end of the drift tubes as shown in Fig; 5 pro ing a. planar equipotentialesurface which results 1n a focusing-5 electric. iieldl. over the: entire; dritt tube gap and prevents divergence of the ion beam as it; crosses the. ga-pf., A very thin metallic `loi-l of low atomic. weight; used' over the-,drift tubeend, in. order tofreducei the scattering effect of; the ion beam as the; ion; beam passes through the foil.

From a practical point of view.,. the extent to which this. means and method of accelerating ionscan` be carried out,l isdependent; onlyupon the physical. length.- to. which the. accelerator; ware guide can be extended, and the amount of power available for driving it. Therefore for a representative arrangement let us consider in detail an ion accelerator 40 feet long designed to operate at approximately 205 megacycles per second with a peak power input of 80 kilowatts per foot using a 150 to 300 microsecond pulse width, and a repetition rate of l5 pulses per second, to produce a beam of ions having energies of the order of 45 million electron volts.

This representative arrangement is illustrated in Fig'. 6 and comprises essentially of the following parts: vacuum tank I3, inner cavity I4, drift tubes I6, radio-frequency oscillators I'I, target chamber I8, Vacuum tank opening mechanism I9,

and a source of ions including an electrostatic generator 2| or other device.

The tank I3 is preferably made as nearly as possible hermetically or vacuum tight in order that the inner cavity I4 can be established and maintained at the desired pressure. Under normal operating conditions the pressure is reduced below that of the atmosphere to a value of the order of 10*4 mm. Hg.

Fig. 7 depicts a longitudinal sectional view and Fig. 9 a transverse sectional view of the vacuum tank or envelope I3, conveniently made up of two metallic half cylinders 22 and 23 and welded or otherwise fastened in airtight fashion to end plates 24 to afford a chamber of cylindrical shape. Neither of these is made much thicker than necessary to resist the inward pressure.

The walls of the tank merge with va iiange 25 adjacent to one terminal of the tank'and with a ange 26 adjacent to the other terminal of the tank. These anges are secured by any suitable `means, such as welding, to the remaining portions of the tank in order to afford a vacuum tight connection therewith. They are each provided with a plurality of fastening bolts 21 and nuts 28 or other releasable fastenings, to clamp the flanges together between a suitable gasket to afford a vacuum tight joint.

The subatmospheric pressure level is established and maintained in the chamber by operation of a vacuum pumping mechanism.

In order to maintain vacua of the orders of magnitude mentioned, the tank I3 is provided with a vacuum connection or manifold 29 in the outer side wall 23 communicating with the chamber 3I and extending to any appropriate type of pump, such as a diffusion pump 32.

Also included in the vacuum system is a mechanical displacement pump 33, acting as a backing pump for the diffusion pump 32 and connected thereto by a conduit 34. The effect of the pumps and appurtenances is to afford a steady, regulated, subatmospheric pressure within the tank I3.

Inorder to open the top half of the vacuum tank 22 for inspection and maintenance of the inner cavity E4 and the drift tubes IS, a hinge 35 is provided. rI'wo hydraulic cylinders I5 actuate the cover 22 and comprise a liquid tight tubej, two cover or end plates 31 and 38, held together by tie bolts 39, a connecting rod 4I, a piston in tube 36 attachedto connecting rod 4I, and a packing gland 42, to prevent leakage of the liquid.

In operation the fastenings 2l and 28 are removed and aliquid is forced into opening Q2; thereby forcing the piston down the cylinder I9 which pulls the vacuum tank cover 22 open on pivot hinge 35. When the cover is all the way 4openholes 44 and 45 are brought into alignment '6 and a slide pin is inserted so the liquid pressure may be removed from opening 43 and the tank cover 22 will remain open. The pivot pin 46 allows the cylinder I9 to swivel as the tank cover 22 is being opened.

The vacuum tank I3 is supported on rollers fil and t8 and is held from any longitudinal travel by the vacuum manifold 23 and 3l which is fastened to the iioor. The vacuum tank I3 rides on these rollers and allows for any thermal expansion which might take place in the tank.

End walls 2'4 of the vacuum tank I3 are provided with iianged extensions 49 and 5I affording communication with external apparatus for entrance and exit of the ion beam.

ThereV is disposed within the tank I3 a liner or inner cavity (Figs. 6, 7, 9,1()V and I4) generally designated I4, symmetrically mounted therein.

The inside of the liner I4 has a twelve sided configuration and is composed of twelve narrow strips of copper 52 riveted, or otherwise fastened together on the edges, the entire structure is attached to a plurality of dural channel shaped rings 53 to afford rigidity to the linear. Copper end plates 59 are riveted and soldered to the side strips 52 which forms a closed cavity of substantially cylindrical shape.

Small angle clips 57.' are riveted to the channel rings 53 and rest upon brackets 58 which are welded to the vacuum tank I3 as to support and maintain the liner I4 in appropriate axial and radial position.

Like the vacuum .tank IS, the upper section of the liner I4 is made removable between the points 54 and 3S to facilitate any work that might have to be done on the interior of the liner.

In order to remove heat that is evolved from the liner` I4 during operation there is provided a cooling iiuid circulating system comprising a number of longitudinal copper cooling tubes BI connected together to water manifolds 62 and 63 which lead outside the vacuum tank I3 to any suitable source of cooling iuid, such as water, under the control of a regulating valve of any standard kind to regulate the water or comparable cooling liquid into the cooling tubes 6I.

Suitable manifolds are provided on the other end of the liner to connect the cooling tubes 6I together to form a passageway for carrying away from the structure the discharged fluid.

Liner strips 52 are formed around the cooling tubes GI as shown in Fig. 13 and united closely together, preferably by means such as solder, copiously applied to increase the thermal path of conduction between the parts. Heat is then more readily transferred from the metal parts of the liner through the walls of the tube to the fluid circulating therein.

In order to facilitate the removal of air and gases from the interior of the liner I4 a number oi` apertures or slots $4 are provided adjacent to the vacuum manifold 2S. Inasmuch as the electrical current flow is longitudinal in the liner lli, it is desirable to make the slots as narrow as possible in the radial direction but it is permissible to allow them to be made long in the longitudinal direction without disturbing the current flow therein.

Pursuant to the invention, there are provided drift tubes I3 shown in Figs. 6, '7, 9, 14 and in enlarged detail in Figs. l1 and l2. The construction of each of the drift tubes I3 is substantially identical with the exception of the diameter which decreases and the length which increases as they are disposed down the length of the accelerator.

7 The drift tube is composed: of a tube 66 in which is solderedA a cap Blf which maintains tube 68 in coaxial alignment with the outside tube |56. On theother end of the o-utside tube t6 is soldered a boss E9 with an internal thread. Cover 'H is threadably attached to the boss 99 and forms a support for the removable ybase portion l2. Removable base portion 'l2 forms a base for the foil holder 'I3y and the foil 'F4 which are held in Aplace by a threaded retaining tube 16. The foil 14, that is used for focusing the ion beam, is

made. from beryllium about 25 millionths of an `inchV thick and is cemented` to the foil holder 73 in order to facilitate the handling ,ofv the foil. When it is desirable to change or substitute a foil itl is only necessary to remove the drift tube l cover 1| and, upon manipulation of the base l2 the entire focusing foil assembly is readily removedV and anotherrentire Yassembly, substituted in a minimum'of time.

Since the drift tubes are disposed in strong radio-frequency fields and are also being bombarded by the ion beam, they are conveniently fabricated of' copper or comparable material which is effective as a thermal and electrical conductor. Inasmuch as the drift tubes operate at an elevated temperature, there is provided means for cooling the drift tubes with a supply of' cooling fluid, such as water, circulating through cooling tube Il soldered directly to the inside of tube 66. Cooling tube 'll connects to main longitudinal fluid manifolds 'It and 'i9 which run to the outside of; main vacuum tank |52 vto an external source. of cooling liquid, not shown.

f Tube 6E isv soldered, or otherwise fastened, to a tubular post 3|, which is fastened to flange plate 82 with an associated threaded stud 33 and a hemispherical ball 84. Mounting plate S5 forms a socket for the4 ball 84 and is clamped between liner anglesv Bl by clamping plate 88 and held in position by screws 89.

To afford a universally orientable mounting, the plate 86 serves as a support for two screw studs 9| and two pressure springs 92, and the projecting portion of each of these screw studs presses on flange plate 82.. In its median position, the flange plate 82 is substantially parallel to mounting plate 86, but it is adapted to move out of parallelism by manipulating screw studs 9|, thus effecting an axial or horizontal adjustment of the drift tube It.. By advancing or retracting the nut 93 and re'adjusting screw studs 9|, a vertical motion of drift tube |6 is accomplished to any desired selected value. To cover the enlarged aperture in liner strip 52 a cover disk 94 is provided and is held in close abutment to liner strip 52y by the collar 95 and the spring 91, thus permitting movement of drift tube post 8 I, while effectively closing the enlarged aperture.

In order to tune the liner or cavity I4 to the required frequency or wave length, there is provided means f'or moving the two similar end drift tubes 99 and 99, preferably in accordance with a very careful electromechanical control.

In order to move the end drift tube, the tube |,0I is freely movable within the flange shell |02 and is provided with a restraining arm |93 engaging a slot in the mounting bracket liti, to prevent any rotation but permit axial movement. Threaded 'sleeve |05 is soldered, or otherwise fastened, to nose plate |07 which is secured to the outer tube lill. Threaded sleeve |05 is engaged by threads on a hubbed worm wheel |98, which is confined against translation in one axial direction by collar |09 and in the other by abut- `conductor rod oscillator circuit, and is provided with a slotted ment between the. hub of the: wheel and. the mounting bracket |04.

The worm wheel |68Y may be rotated by virtue of its engagement with a worml made fast on a shaft |I2. The shaft II2 is journaled in bearings H3 which are fastened on mounting bracket |04. The worm being fast on shaft H2, rotates therewith when the shaft is rotated by the electric motor H4. Upon energizing the motor H4 in the desired direction the shaft ||2 and worm ||I rotate and turn the worm wheel |09, thus advancing or retracting the end drift tube 98 in the desired axial direction. Y

Although it may be preferable to excite the accelerator with a single highy power oscillator, there is illustrated and described an accelerator which is excited with a multiplicity of lower powered oscillators each coupled at proper intervals along the length of the accelerator wave Y guide. Furthermore, as an expedient thirty lower power oscillators carrying the designation Signal Corps BC-677 Radar Transmitter are utilized. Each rada-r transmitter Il is a complete push-pull-parallel type oscillator utilizing four forced air cooled triode vacuum tubes with a peak power output of about 100 kilowatts, at 205 megacycles per second. All thirty oscillators are pulsed simultaneously and in synchronism from a common power source, thus being in effect one large high powered oscillator. The frequency of oscillation of the oscillators is dependent on the resonant frequency of the accelerator cavity, there-fore all oscillators wil-l be operating on an identical frequency.

Power from the oscillators ll is fed to the accelerator through a coaxial transmission line llt to a coupling loop lil within the liner or cavity lli shown in enlarged detail in Fig. 13. In order to provide a vacuum tight entrance for the transmission line llt, an extension tube Illiis welded to the side of the tank wall 23., and tube H8 is provided Kwith a flanged extension H9, welded thereto. Tube I2! forms the outer conductor of the transmission line and is fastened to the oscillator side |22, to form a rigid extension.Y Inner |23 is attached to the internal friction pin |24, which engages a hole in conductor |2, thus forming a removable electrical connection'therewith. Outer conductor |2| is providedv with a. flangeI plate |21 and an internally threaded flange nut |28, threadably attached to the threaded coupling |25, thus forming a rigid junction mechanically and electrically between tube 52| and extension tube |3|. Inner conductor |26 is bonded to a glass insulator |32 forming a vacuum tight joint. Coupling loop Ill' is soldered to conductor |25 and is contoured in the shape of a semicircle and is returned and soldered to outer tube |33, forming a complete electrical circuit. Glass insulator |32 is bonded to tube |93 to form a complete vacuum tight seal, after which extension tube |3| is soldered to tube |33 thereby forming a rigid connection. f

Tube |33 is hard soldered to a cover plate |34 which is bolted to flange |'9 with a suitable rubber gasket its therebetween to form a vacuum tight joint when bolts '|31 and nuts |38 are tightened.

An aperture of elliptical contour is provided in liner strip 52 for the admittance of coupling loop Ill.

Axially mounted on flange 5| of tank I3 is a vacuum tight target chamber generally designated i8, shown in vertical cross section, in Fig. t.

The stream of ions after being accelerated by the accelerator are received by the target chamber I8 and impinge on a target |39 which is insulated from the target face plate IllI by inn sulator disk |42. A vacuum tight electrical feedthrough insulator |43 connects to the target |39 and to an external electrical conductor ille Which emerges to a remote instrument or meter, not shown, so that the ion beam current can be ndicated or registered.

Inasmuch as the target |39 and target face plate I4! are under direction bombardment, there is provided means for cooling `the face plate I4! by cooling tube |45 which is thermally united to the face plate by copious amounts of solder. Cooling fluid or liquid, such as Water, is circulated through the cooling tube |46 at a suiiicient rate to maintain the temperature of the parts below a selected maximum value.

Face plate IGI and its associated parts is clamped to target chamber I8 by a multiplicity of studs |41 and tightened against gasket |45 by nuts |49 thereby aiording a vacuum tight junction, yet the entire face plate I4! is readily removable for changing or substitution of targets.

When the target assembly is removed it is highly desirable that the main tank I3 is not let down to atmospheric pressure, therefore a closeable gate I is provided. Gate |5| is mounted on a shaft |52 which extends outside of the chamber i3 through a suitable packing gland to a suitable actuating mechanism, not sho-wn, which when energized will close the gate |5| against gasket |53 and the chamber I8 affording a vacuum tight seal.

Vacuum chamber I8 is provided with a flanged extension |54 which is bolted, or otherwise fastened, with releasable fastenings, to flange 5| to make a rigid vacuum tight junction and support for the target chamber and its associated parts.

Flanged tube |55 provides a vacuum tight connection from flange 49 on tank i3 to a suitable flange on the source of ions, such as the electrostatic generator 2 I.

In operation of the accelerator, the oscillators are energized to excite the wave guide |45. Ions from a source thus enter the Wave guide and start along the axis thereof. The ions are .grouped into synchronized pulses and are made to enter the accelerator system at the proper tim to achieve phase stability.

After the ions enter the Wave guide, they are accelerated along the axis of the Wave guide through the drift tubes until they reach the target |39, receiving an additional acceleration Y as they pass through each drift tube in the Wave guide.

The design of the drift tubes depends upon the velocity with which the ions enter the Wave guide. An electrostatic generator can be used for example as a source of potential to produce initial accelerations of four to four and one half million electron volts.

While the invention has been described with particular reference to the acceleration of ions, it will be appreciated that it is also applicable to the acceleration of electrons or other electrically charged particles.

It Will therefore be understood that this invention is not to be limited to the details of the structure and methods of operation hereinabove described but that many modications may be made in the apparatus and method within the scope of the following claims.

What is claimed is:

l. An apparatus for accelerating high velocity ions comprising a Wave guide, a radiofrequency generator for energizing said Wave guide to produce a longitudinal electric eld therein, a series of graded length drift tubes spaced apart to form gaps disposed within said wave guide along the longitudinal axis thereof, said drift tubes also having graded diameters thereby establishing said longitudinal electric iield in a uniform manner throughout the entire length of said wave guide, means for axially introducing high velocity ions into said Wave guide whereby said ions will be further accelerated uniformly through the entire length of said wave guide.

2. A linear ion accelerator comprising a hollow elongated substantially closed wave guide, a series of coaxial tubes disposed Within said wave guide along the axis thereof, a radio-frequency generator for exciting said wave guide to produce an axial electric field therein, means for injecting ions into said wave guide at the increasing voltage portion of the excitation cycle thereby producing a phase-stabilized ion beam accelerated through said coaxial tubes, and a thin metallic foil covering the entrance end of each of said coaxial tubes thereby establishing the electric eld in a desired fashion to control said phase-stabilized ion beam divergence.

3. An apparatus for accelerating high velocity ions comprising a Wave guide, a means for energizing said wave guide, a series of drift tubes spaced apart to form gaps disposed Within said wave guide along the longitudinal axis thereof, and means for altering the length of the rst and the last drift tube of said series thereby tuning said Wave guide to a predetermined frequency Whereby high velocity ions are further accelerated.

4. An apparatus for accelerating high velocity ions comprising a hollow elongated substantially closed wave guide, a series of coaxial tubes, said coaxial tubes being graded smaller in diameter and longer in length as they are disposed within said Wave guide along the longitudinal axis thereof and spaced apart to form gaps, a plurality of simultaneously pulsed radio-frequency generators, a plurality of coaxial transmission lines associated With said radio-frequency generators and each having an outer conductor connected to the Wall of said wave guide and an inner conductor entering the interior of said wave guide in the form of a coupling loop whereby said radio-frequency generators energize said wave guide to produce a uniform axial electric eld therein, means for axially introducing ions into said coaxial tubes at the proper phase of oscillation of said radiofrequency generators thereby producing a phasestabilized ion beam subjected to repeated acceleration as it crosses said gaps, means for shielding said ions from the decelerating e'ect of the electric field in the reverse half cycle of said radio-frequency generators, a thin metallic foil covering the opening at the entrance end of each of said coaxial tubes to form the electric field in said gaps in a predetermined fashion to control the divergence of said ion beam.

5. An apparatus for accelerating high velocity ions comprising a hollow elongated substantially closed Wave guide, a series of coaxial tubes, said coaxial tubes being graded smaller in diameter and longer in length as they are disposed Within said Wave guide along the longitudinal axis grass-s thereofand spaced, apart troform gaps, a rplu- 'ral-ity of simultaneously pulsed radio-frequency generators, a'plurality of `coaxial transmission ll'ines associated with said radio-frequency generators and each having an louter conductor con- ?nected to the wall of said Wave guide `and an inner conductor entering fthe interior of rsaid waveguide in the form of a coupling loop wherebyf'said radio-frequency generators energize said wave guide to produce a uniform axial electric 'deld therein, .a source of high velocity ions including Ian electrostatic generator, means for faxiallyzintro'ducing said ions into said coaxial ftubes' at the proper .phase of oscillation of said vradio-frequency .generators thereby producing a phase-stabilized ion beam subjected to repeated 'acceleration las it crosses'said gaps, means for Y :shielding said ions .from .the decelerating effect of the electric ield in the reverse half cycle of 'said radio-frequencis7 generators, a thin metallic foil covering the opening at the entrance end oi' each of said coaxial tubes to form theelectric i'le'ld in said .gaps in a predetermined fashion -to control the divergence of said ion beam.

.6. An .apparatus for Yaccelerating high velocity and means for axially introducing high velocity ions into said wave .guide whereby said ions will be further accelerated uniformly through the entire length of "said wave guide.

7. An apparatus for accelerating high velocity ions comprising a wave guide, a radio-frequency generator for energizing said Wave guide to produce a longitudinal electric field therein, a series of drift tubes 'spaced apart -to form gaps disposed Within said Wave guide valong the longitudinal axis thereof, a Iplanar ion transparent surface .covering the entrance end of each of -said'drift tubes, vand means for introducing high Velocity ions. axially into said Wave guide during the increasing voltage portion of the energization cycle whereby said Vions will be .further accelerated yand .focused 'for the entire length of said wave guide. v

5.` An apparatus Afor accelerating vhigh velocity ions comprising a wave guide, a radio-frequency generator for 'energizing .said waveguide to produce va longitudinal electric kheld therein, a series of drift tubes spaced apart to Yform gaps disposed within said Wave guide along Vthe longitudinal axis thereof, said drift tubes vhaving graded diameters thereby establishing said longitudinal i2 electric' Held .in a uniform manner'throughout the entire length of saidv waveguide, a planar ion transparent surface vpositioned .parallel to and in close proximity .to the entrance 'end of said drift tubes so as to impart a focusing'action to said longitudinal electric field across said drift tube gaps, and means .for introducing high velocity ions axiallyfinto said wave guide whereby said ions 'will be further accelerated and focused uniformly for the entire length of said wave guide.

9. An apparatus in accordance with claim' f1 wherein said drift tubes have respectively A.increasing diameters from said ion introducing means for establishingfsaid longitudinal electric eld in a uniform manner 'throughout 'the entire length of said Wave guide.

10. An Aapparatus .in accordance with claim 7 wherein said drift tubes have .respectively decreasing length irom said ion introducing means, the first and last of said drift tubes being adjustable in length for tuning said wave guide to a predetermined frequency.

11. An-apparatus for accelerating high velocity ions comprising a hollow elongated substantially closed wave guide, a series of coaxial tubes disposed in spaced apart relation Within said vwave guide valong the longitudinal axis thereof, said coaxial tubes being graded larger in diameter and shorter in length from one end to the other of said wave guide, a plurality of synchronized radio-frequ'ency generators, a `plurality of coaxial transmission lines connected at one end to said generators and having a coupling loop at the other end extended Within said wave guide to produce a uniform axial electric neld therein, means for axially introducing ions into the coaxial tube having the smallest diameter and longest length during the increasing volta-ge portion of said axial electric held, 'a thin metallic foil disposed across the entrance opening of each of said coaxial tubes, and means for altering the length of the-:first and last coaxial tube.

LUIS W. ALVAREZ.

REFERENCES CITED The following references are of .record in 'the file of this patent:

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